Windows Vista 32 or 64 bit for Pentium 4 640

[Mirey86]

Hi everyone,

I am planing on upgrading my computer to vista home premium and was wondering if I should install the 32 or 64 bit upgrade version here is my system:

Motherboard: Intel 915pbl
Processor: Pentium 4 640 (EM64T)
Video: Sapphire 3870
Ram: 2X512gb & 2x1gb
Sound: Onboard

I know my processor as some sort of 64 bit capability but still wondering if going with a 64 bit version of vista would be worth it?

Thanks in advance for your help.